Sure, a programmer can add HP and maybe mileage, but, if the tune is keep moderate, will the engine longevity be effected for better or worse? I know that unprepared dummy who goes all out on the tune will blow gaskets and/or the tyranny, but I mean a moderate tune with basic intake and exhaust mods.... Will this decrease engine life?

 

As long as its maintained IMO no not at all it will continue on as business like usual

 

I agree with red rattler, if you keep up with maintenance like fuel filters oil changes it would not hurt anything.

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A good tune should lower EGTs; high EGTs reduce engine life. Not all tunes are good tunes, so not all tunes will promote engine longevity.